Although the present invention is believed to be applicable to different types of scroll machines it is disclosed herein embodied in a refrigerant compressor for use in air conditioning, heat pump and refrigerating systems, such as that disclosed in applicants' assignee's U.S. Pat. No. 5,102,316, the disclosure of which is hereby incorporated herein by reference.
In the marketplace there is an increasing demand for much quieter machinery than was hitherto acceptable, and this is especially true in the case of air conditioning and heat pump systems. There are a number of identified sources of sound in a scroll compressor, many of which are relatively easily cured. A recently discovered source of sound which does not lend itself to easy cure, however, concerns the mechanical impact noise or rattle which is caused by vibration of the orbiting scroll member and Oldham coupling under certain operating conditions, i.e., under lighter load conditions when there is insufficient loading of the orbiting scroll and Oldham coupling to prevent force reversals which can cause the keys on the Oldham coupling to impact noisily on the sides of the slots in which they are disposed.
Even though scroll compressors have been in commercial production for many years now, it has been observed that some compressors are significantly more quiet than others. In studying this phenomenon it has been determined that the variance in the noise in question is in large part due to the variance in physical dimensions resulting from the difficulty in closely controlling manufacturing tolerances to a precise degree. The problem has been compounded by a lack of understanding of exactly what specific dimensions and tolerances are in fact critical to noise attenuation in such a machine.
Conventional wisdom dictates that each of the mating scroll wraps has a true involute profile which is generated from the exact same size and shape generating element and the same initial swing radius. In other words, there should be zero generating radius bias and zero initial swing radius bias. In addition, the mating scroll wraps should be arranged at exactly 180 degrees with respect to one another. In a theoretically perfect machine built to such absolute dimensions, the wraps would be fully conjugate and loading would be symmetrical. This is a "nominal" design as discussed herein. Because it is physically impossible to manufacture anything to an absolute dimension on a repeating basis, the challenge is to know where to target nominal dimensions and how to specify tolerances in such a way that the desired goal will be obtained.
The present invention resides in the discovery of what is truly critical to the design of a quiet scroll compressor (insofar as the present noise source is concerned), how to specify the critical relationships of the parts, and where to focus the unavoidable tolerances so that the desired overall result will be obtained, without sacrificing efficiency and without increasing production cost.
Applicants' have discovered that noise associated with the vibration of the orbiting scroll and Oldham coupling in a scroll compressor can be related to the moment load about the center of the orbiting scroll. When this moment is sufficiently large, noise problems associated with the vibration of the orbiting scroll can be avoided, but when this moment becomes too small, significant noise problems will occur. The moment on the scroll is a function of the operating condition and compressor design. The objective of this invention is to provide for optimal moment loading by biasing flank contact through the proper selection of two compressor design parameters, i.e., the initial swing radius bias and the generating radius bias. These two parameters alter the moment loading on the orbiting scroll by changing the scroll contact forces (flank forces) and by introducing additional gas forces (leakage forces). Several unique methods of fabricating scroll compressors to avoid the problems of the prior art and achieve the objects of the invention are disclosed, as well as several novel physical designs for achieving the same result.
The preferred approach herein is to increase the moment loading on the orbiting scroll and Oldham coupling using the flank loads while minimizing the contribution from adverse leakage forces. One preferred way of implementing this approach is to provide a moderate positive initial swing radius bias combined with a small negative generating radius bias. Here the positive initial swing radius bias provides the increase in moment due to flank forces and the negative generating radius bias minimizes leakage forces. The advantages of this implementation are: The initial swing radius bias is the primary parameter and is more controllable in manufacturing than the generating radius bias; the initial swing radius bias can be introduced in a number of ways, whereas the generating radius bias must be machined into the scrolls; the negative generating radius bias will reduce the leakage at suction which is important for reducing the adverse effects of leakage on capacity. A small generating radius bias combined with flank flexibility leads to better load sharing, thereby reducing problems associated with large localized contact loads.
Another preferred way of implementing this approach is to provide a large positive generating radius bias in combination with a small negative initial swing radius bias. This approach is more general and if multiple generating radii are used on a single wrap it is possible to use both flank forces and leakage forces to load the scroll. Using this multiple generating radii approach it is also possible to avoid problems associated with outer wrap interference at suction closing, i.e., "suction bump".
Other features and advantages of the embodiments of the present invention include the provision of a scroll machine design and method of fabricating such a machine which provides significant and consistent improvements in sound attenuation without sacrificing efficiency, simplicity in design and cost of manufacture.